because I think that when someone says "kids", they mean someone younger than them (in age or mentality) And if they want to talk about people who are not younger than them or older, then they would be saying, "I like people, that are of my age".

Also he gave the reason, "tiny and cute". An older person stating that.... to someone it may sound "pedo-ish". But then in normal circumstances it would be taken purely innocently or enthusiastically... basically less sexualized and more as in, "the person is babysitter material" but we don't know that about Spirit as he only stated that he liked kids and not the other way around... because that would make things completely "consensual" (Still wrong from some standpoint but meh Laws)

And then there's Illya, who just wants any chance to derail Spirit from achieving any happiness for the fun of it.